The case for the college premium confuses chickens and eggs, responds Richard Vedder, a Ohio University economist, on the College Affordability site.

Those who go to college are, on average, brighter, more knowledgeable, more disciplined, and more conscientious than those who go to work after higher school. . . . Even if those in the college going population had NOT gone to college, they would have earned more than those others who did not go on—simply because they are better workers.

The college premium varies significantly by field of study, the Georgetown report finds. For example, 28 percent of workers with an associate degree earn more than the median wage for four-year college graduates. There’s a high premium for a degree in engineering, not much for social work or early childhood education.

The Georgetown report only looks at graduates: Forty to 50 percent of college enrollees don’t complete a degree, Vedder adds.

There is a substantial risk element to making a college investment, particularly those with attributes (low high-school grades, poor test scores, etc.) that suggest the probability of dropping out is high. Adjusting for this risk factor lowers the expected income gains from college dramatically.

In addition, as more Americans enter the labor market with college degrees, the payoffs are likely to change, writes Vedder, who predicts diminishing returns for a college degree.

A growing proportion of new college graduates are taking jobs that don’t require a degree. While they may earn more than co-workers with high school diplomas, their college premium will be reduced.

Finally, a degree’s value depends on the college’s reputation, Vedder points out. The Harvard premium is high. Chicago State? Not so much.

“We need the IRS to provide us average earnings data by college to help evaluate the differential rate of return on investments in the various colleges,” Vedder writes.

Looking at those graduating from high school, I would guess somewhere between 25 and 40 percent should go to four-year schools, because they have the relatively high grades, tests scores, innate intelligence, ambition and motivation — good predictors of college and often vocational success.

The other 60 to 75 percent should pursue less-risky options, Vedder advises. That includes community college or a career college offering specialized occupational training.